Conventionally, since a high temperature, high pressure combustion gas passes through a turbine of a gas turbine, which is used in the generation of electrical energy, etc., it is important to cool a ring segment and the like in order to continue stabilized operation. In particular, due to improvements in the thermal efficiency of gas turbines in recent years, the temperature of combustion gas continues to increase, and it is necessary to further strengthen cooling capacity.
FIG. 6 is an overall configuration diagram of a gas turbine. A gas turbine 1 is made up of a compressor 2 compressing air for combustion, a combustor 3 injecting a fuel FL into the compressed air sent from the compressor 2 and combusting the injected fuel FL to generate combustion gas, a turbine 4 installed downstream of a flow direction of the combustion gas of the combustor 3 and driven by a combustion gas FG leaving the combustor 3, a generator 6, and a rotating shaft 5 integrally coupling the compressor 2, the turbine 4, and the generator 6.
FIG. 7 is a cross-sectional view showing an internal structure of the turbine 4 of the gas turbine 1.
The gas turbine 1 supplies the combustion gas FG generated in the combustor 3 to turbine vanes 7 and turbine blades 8, and causes the turbine blades 8 to rotate around the rotating shaft 5, thereby converting rotational energy into electrical power. The turbine vanes 7 and the turbine blades 8 are alternately disposed along the flow direction of the combustion gas FG. Moreover, the turbine blades 8 are disposed in a circumferential direction of the rotating shaft 5, and thus rotate together with the rotating shaft 5.
FIG. 8 is a cross-sectional view of essential portions of a conventional ring segment. A ring segment 40 is made up of a plurality of segment bodies 41, and is formed around the rotating shaft 5 in an annular shape. Each segment body 41 is supported by a casing 47 via hooks 42 and isolation rings 46. Moreover, a collision plate 44 that is supported by the isolation rings 46 is provided with a plurality of small holes 45. Cooling air CA supplied to the casing blows from the small holes 45 in a downward direction, thereby performing impingement cooling on a surface of a main body (bottom surface) of the segment body 41. In the segment body 41, a plurality of cooling passages 57 and 58 is formed in an axial direction of the rotating shaft 5 toward upstream- and downstream end faces of the flow direction of the combustion gas FG. The cooling air CA after the impingement cooling flows from the interior of the main body of the segment body 41 to the upstream and downstream sides of the axial direction of the rotating shaft 5 via the cooling passages 57 and 58, and then performs convection cooling on upstream- and downstream-end portions of the segment body 41. Moreover, the ring segment 40 is disposed on the outer circumferences of the turbine blades 8, and a fixed clearance is formed between the ring segment 40 and the tip of each turbine blade 8 so as to avoid mutual interference.
As shown in FIG. 9, the segment bodies 41 adjacent to each other are disposed such that end portions 51 and 52 thereof are opposite to each other. Moreover, the turbine blades 8 rotate around the rotating shaft 5 in a right-to-left direction on the sheet surface of FIG. 9 (a rotation direction R). Furthermore, to prevent the combustion gas FG from leaking from a gap between the end portions 51 and 52 to the casing, a seal plate 53 is inserted into the end portions 51 and 52 in the axial direction of the rotating shalt 5.
For this reason, the high-temperature combustion gas ingested by the rotation of the turbine blades 8 stays on the inner circumference of the seal plate 53. Thereby, an outer surface temperature of the segment bodies 41 is raised, and thus oxidation thinning easily takes place at a corner portion of each segment body 41. To avoid this phenomenon, cooling passages 55 and 56 are disposed on opposite sides of the end portions 51 and 52 of the neighboring segment bodies 41 such that the cooling air CA collides with the end portions 51 and 52 opposite each other.
That is, the cooling passage 55 is disposed in the end portion 51 which is front side in the rotation direction of the rotating shaft 5, and thus the cooling air CA, which has performed the impingement cooling on the main body of the segment body, is supplied to blow into the combustion gas of the gap G between the end portions 51 and 52 via a cavity 54. On the other band, the cooling passage 56 is also disposed in the end portion 52 which is rear side in the rotation direction of the neighboring segment body 41, and thus the cooling air CA after the impingement cooling blows into the gap between the end portions 51 and 52. The cooling passages 55 and 56 of both of the end portions 51 and 52 are disposed for blowing toward the corner portions of the lower sides of the end portions 51 and 52 of the segment bodies 41 adjacent to each other. By combination of the cooling passage 55 of the front-end portion 51 and the cooling passage 56 of the rear-end portion 52, each of the end portions 51 and 52 undergoes convection cooling, and a stagnant gas in the gap between the end portions 51 and 52 is purged into the combustion gas FC; and cools an atmospheric gas to prevent oxidation and thinning of the corner portions of the end portions 51 and 52 of the segment bodies 41.
An example of the cooling system of the ring segment described above is disclosed in Patent Document 1.